In fields involving flowing fluids for industrial applications, such as slurries, liquids, chemical, paper, pulp, petroleum, gas, pharmaceutical, food, mining, minerals and vapors and gasses in refinery, it is sometimes beneficial to know certain characteristics of the flowing fluids. For example, in the petroleum industry in which billions of dollars of crude oil are fiscally measured each day on its way from the well heads to the refineries, the volumetric flow rate is a critical measurement in process control and optimization. Unfortunately however, large amounts of hydrocarbons tend to be present in crude oil and as such, during transport between the well heads and refineries the crude oil has a propensity to ‘out gas’ during transport resulting in small, unknown levels of entrained gases being present at fiscal measurement locations. This is undesirable for at least two (2) reasons.
First, because the effect of entrained gases on most known liquid volumetric technologies results in an over reporting of the liquid component flow rate by an amount equal to the volume of the entrained gases, the measured volumetric flow rate is typically inaccurate. In fact, standards have been imposed for volumetric flow. Unfortunately, however, while most standards for fiscal volumetric flow of liquids require that the liquid be completely devoid of gases, a problem arises when it becomes impractical to ensure that the liquid stream in question is indeed completely devoid of free gases. This is because although the gas volume fraction (GVF) level is typically less than 1%, it is often the primary source of error in fiscal measurement. Second, because the complete separation of the gas and liquid phases cannot be ensured, the liquid volume determination is also typically inaccurate resulting in an inaccurate water cut value. Thus, it is reasonable to expect that the more characteristics that are known about the flowing fluid, the better chance there is of effectively measuring, controlling, and optimizing the processing of the flowing fluid.
Accuracy of oil production measurement is typically limited to three constraints. One constraint is the inability to ensure complete separation of gas and liquid flow. This constraint results in inaccurate liquid volume determination, inaccurate gas volume determination, and inaccurate watercut determination. The second constraint is the relatively low number of flow measurements. This is not only due to the installation and maintenance requirements for each measurement device, but also to the affect each measurement device has on the fluid flow, such as an associated pressure drop. As such, increasing the number of measurement points causes a corresponding increase in the total associated pressure drop as well as an increase in the number and costs of installation and maintenance requirements. The reason is maintenance requirements, installation requirements and pressure drop in the point with any increase in measurement points. The third constraint is the very low number of watercut measurement points. This low number is due to the reliability of watercut measurement devices and the calibration requirements of the meters.
Thus, it would be advantageous, particularly in the oil and production field, to have a reliable, non-intrusive, clamp-on apparatus capable of measuring the parameters of an aerated multiphase fluid flow, such as the volumetric flow rate of the liquid of the process flow, the gas volume (or void) fraction of the flow, the watercut of the flow, and the volumetric flow rate of each of the phases of the flow. The present invention provides such an apparatus.